Casting processes use a wide variety of materials which, when in a molten state, can be charged into a flask or mold to produce a part of a desired configuration.
Ferrous castings are used for a wide variety of applications throughout the manufacturing industry. The most common of the ferrous casting materials is gray iron which has graphite dispersed in flake form. It is readily produced at a low cost and displays good strength and excellent machinability for wide usage. Ductile iron, or nodular iron, contains graphite in spherical rather than flake form. Ductile iron exhibits high tensile strength, ductility and resistance to shock.
In general, ferrous castings are formed in a flask or mold having a top half called the cope and a bottom half called the drag. The flask is placed over a part pattern and filled with slightly moist, compactible sand, known as green sand. The flask is then jolted to settle the sand and a high pressure hydraulic press compacts it until it is firmly packed and uniformly hard. The part pattern is then removed, leaving an impression in the sand which forms the outside features of the part.
Inside features of a part are formed by the placement of core assemblies in the mold at the desired locations. Cores are specially shaped pieces of hard-cured sand formed in a separate mold called a core box. The shape of the core is defined by the inside cavity of the core box as modified by the selective placement of loose pieces within the core box.
After the core assemblies are placed in the mold, the cope and drag are placed together forming a mold joint called a parting line. Upon closing, the mold is ready to receive the molten iron. After pouring, the cast part is cooled and removed from the mold for finishing.
It is sometimes desirable to incorporate a separate functionally movable element within the cast part. Such `cast-in` elements generally reduce the number of manufacturing and assembly steps required to produce a functional subassembly. Cast-in parts can be made of material either like or unlike the material used to form the cast portion. When like materials are used, the cast-in part can be coated with silica sand to prevent bonding between the cast-in part and the casting. When dissimilar materials are used, coating may not be required since shrinkage of the cast portion upon cooling can provide adequate clearance to allow movement of the cast-in part.
Although rotatable rollers and enlarged ends of rotatable shafts have been cast-in metal castings, heretofore, a spherical ball having a central opening therethrough has not been cast-in an annular ring such that the ball is able to freely rotate about its center in any direction.